This project seeks to determine the location and mechanism of neurotransmitter secretion and reception. Rapid freezing and subsequent freeze-fracture of synapses exposes fleeting structure changes in the cell membrane accompanying discharge of synaptic vesicles. This approach has shown that each quantum of transmitter is released by one synaptic vesicle. Structural details which may be specific for different pharmacological types of synapses are being investigated by examining postsynaptic membrane structure. New methods are being developed to use rapid freezing to localize calcium in neural tissue in different states of activity, in order to define its role in controlling these states. This work is significant in that it defines the normal structure of synapses and relates normal variations in structure to different functional states. Thus, it becomes possible to distinguish pathological changes in structure, an issue of great importance in studying the etiology of epilepsy or myasthenia gravis. The current program also include freeze-fracture of developing synapses, which will aid in understanding of both normal development and developmental failures in the brain and peripheral nervous system.